Password Protect ONE Page and https issue

Hi
I have one page on a site I wish to protect. It has a video on it. I have used WordPress visibility window set to Password Protect to keep it private. All works in http. But the site is know made to work in https and its not working. The password enter page just reappears when you enter the password. I don’t know if this makes a difference but under general settings in the admin area the url and web address are different.

I’m wondering if anyone knows the reason for this and if they know how to fix it.
I don’t require a membership plugin. I just want to give people a password that when they enter – they get to see the contents of that page.

And its just one page I want to protect – not the whole site.

Thank you in advance.